A cup of this kind is prior art in Japanese published patent application JP2001-192015A. The bottom skirt of the known cup widens out downwards. The widening serves to fix an outer sleeve, which surrounds the interior defining sleeve by forming a hollow space. As the widening of the bottom skirt defines the distance between the inner sleeve and the outer sleeve, the widening of the bottom skirt along the periphery must be continuous. A partial widening of the bottom skirt is not possible. The outer sleeve is placed around the bottom skirt, folded inwards and attached thereto. When the outer sleeve is being attached to the bottom skirt, it may occur that the liquid tightness of the bottom skirt is affected. The attaching of the outer sleeve by means of folding is very complicated.
In the case of the known cup, the outer sleeve surrounds the bottom skirt completely, so that this can no longer be seen from the outside. When the outer sleeve is folded inwards and attached from the inside to the bottom skirt, counter-holding from the outside is no longer possible. The outer sleeve can only be pressed against from the inside with a very low level of force, which the bottom skirt can take up itself. If the pressure force is too great, the bottom skirt may tear; on the other hand, the attaching of the outer sleeve can be inadequate if the pressure force is too low. In the case of attaching the outer sleeve by means of heat sealing it can occur that the sealing between the bottom skirt and the sleeve defining the interior dissolves, as when the inwardly folded outer sleeve is being sealed, no counter pressure can be exerted from the outside on the bottom skirt.
In the case of cups made of paper material, the bottom skirt is a very important element of the cup. The bottom skirt is necessary for the connection between the sleeve and the bottom. At least two material layers are disposed in thickness direction on top of one another, namely the material of the bottom and the material of the interior-defining sleeve. The bottom is advantageously pot-shaped, whose open side faces away from the filling opening of the cup. The at least two material layers are advantageously arranged along the wall of the pot-shaped bottom. It can be additionally provided that for example the sleeve is folded inwards around the material of the bottom, and that the bottom skirt consists of three or more material layers. The material of the bottom is glued or sealed to the material of the sleeve in the area of the bottom skirt, in order that it is liquid-tight for at least a certain time.
The term “paper material”, from which the bottom and the sleeve are made, includes various material, which comprise at least one layer of paper, paperboard or cardboard. In addition the material can comprise one or more layers made of synthetics and/or aluminium. It can also be provided that the paper material is waxed or coated, in order to provide a resistance against the liquid with which the cup is subsequently filled. The paper material is advantageously coated at least on the side facing the interior with a thin synthetic layer, preferably made of polyethylene. In contrast to purely synthetic material, the formability and in particular the ductibility of such paper material is limited. In the case of too great a deformation, the paper material itself, or a provided coating, may tear, so that the liquid-tight properties are impaired. The bottom skirt is therefore an essential design feature in the case of cups made of paper material and cannot be omitted.
It is an object of the present invention to simplify the producibility of a cup of the above mentioned type and to avoid difficulties with liquid-tightness at the bottom skirt.
This object has been achieved in accordance with the present invention in that the sleeve and/or the bottom in the area of the bottom skirt and/or the bottom skirt itself comprises at least in an area along the periphery an outwardly projecting widening, and in that a lower edge forms a standing surface for the cup.
The object has been achieved in accordance with the process according to the present invention in that a semi-finished product being essentially liquid-tight and comprising a fillable interior is used, in which the sleeve and/or the bottom in the area of the bottom skirt and/or the bottom skirt itself is widened outwards in at least an area along the periphery.
The standing surface of the cup is enlarged by means of the widening, even if the widening is only partial, so that the cup acquires an improved stability. The widening is hereby not covered, or not completely covered, by an outer sleeve, so that the material of the sleeve or the bottom directly forms the standing surface. The bottom skirt thus cannot be impaired in its thickness by the application of additional material of the outer sleeve. In an advantageous embodiment, the widening is continuous and formed uniformly along the periphery. When the paper material is coated, it is advantageous to form the widening only to the point where the coating does not tear.
As a semi-finished product is used, in which the bottom and the sleeve are attached liquid-tight together in the area of the bottom skirt, the widening can be formed at the bottom skirt without impairing the liquid-tightness of the bottom skirt. It can be advantageous to use a semi-finished product in which the bottom skirt, as seen in axial section, extends essentially parallel to the middle axis of the cup, in which in the case of a round cup cross section, the bottom skirt extends essentially cylindrically. It can also be provided that the widening takes place only partially in an area along the periphery. In the case of a bottom skirt which no longer tapers, or of a partial widening, the paper material requires less elongation and the danger of tear formation is reduced. The stability of the cup can nevertheless be increased by means of an enlarged standing surface.
In an advantageous embodiment of the present invention, the bottom skirt is not widened in its entire height. The area of the bottom skirt bordering the bottom remains in its original form, while the lower edge of the bottom skirt is widened. The height of the widening at the bottom skirt can hereby correspond to approximately half the height of the bottom skirt. The bottom skirt then comprises, as seen in axial cross section, varying angles of inclination to the middle axis of the cup, whereby the bottom skirt in the area of the lower edge widens out at an enlarged angle of inclination. The bottom skirt comprises two different height areas which fulfil different functions. The upper height area serves to seal the fillable interior and attaches the conical sleeve essentially liquid-tight to the bottom. In the lower height area of the bottom skirt, the material of the sleeve defining the interior and/or the wall of the bottom is widened and forms with its lower edge an enlarged standing surface for the cup. In this height area a liquid-tight connection between the material of the bottom and the material of the sleeve is no longer absolutely necessary.
It can be advantageous that the material of the sleeve or of the bottom in the area of the bottom skirt, at least in the area of the lower edge, is warmed up before and/or during the widening process. Warming up can for example take place by means of blowing the bottom skirt with hot air or by means of a heated widening tool. The temperature is advantageously so chosen that a synthetic layer present on the paper material does not reach its melting point, but rather only becomes somewhat softer.
It is advantageous when the widening tool comprises at least two elements, of which one widens the bottom skirt from the inside, while the second acts as a counter tool and counters from the outside. This ensures that even in the case of a warmed-up bottom skirt, the liquid-tight connection between sleeve and bottom does not dissolve. Both elements of the widening tool can consist for example of radially movable jaws, axially movable mandrels or of rollers running along the periphery of the bottom skirt.
The cup according to the present invention is very versatile, as it can be applied without an outer sleeve, or with a variety of different outer sleeves. A heat-insulating sleeve is advantageously provided, which surrounds the interior-defining sleeve while forming a hollow space. The outer sleeve is hereby advantageously slid onto the conical interior-defining sleeve along the middle axis and fixed, before the bottom skirt is widened.
The widening on the bottom skirt can be applied very advantageously in order to improve the stacking properties of the cup. A stackable cup is for example known in European patent EP 1 227 042 B1. The interior-defining sleeve of the known cup comprises a first means for holding another cup of the same type. The known cup comprises a second holding means on an outer sleeve, which surrounds the interior-defining sleeve with a heat-insulating hollow space. The second holding means is formed by a curled part rolled inwards and applied to the lower end of the outer sleeve. When the cups are stacked, the second holding means applied to the outer sleeve can act together with a first holding means applied to a similar cup. A number of cups stacked on top of one another form hereby a stable stack, in which the stacked cups rest securely on top of one another, without however wedging in each other. As wedging of the stacked cups is prevented, the individual cups can therefore be very easily removed from the stack.
The known cup has the disadvantage in that the forces occurring in stacking are relayed through the interior-defining sleeve and through the outer sleeve. The forces, which must be relayed within the cup from the first holding means to the second holding means, are first transferred through the interior-defining sleeve to connecting points between the inner sleeve and the outer sleeve and relayed via these connecting points to the outer sleeve. In the outer sleeve the forces are relayed to the second holding means formed as an inwardly rolled edge and there transferred to the next cup. The inner sleeve and the outer sleeve must be sufficiently stable in order to take up the occurring forces. In addition, the connecting points between the outer sleeve and the inner sleeve must be designed to take up the maximum occurring forces.
The scope of the design of the cup according to European patent EP 1 227 042 B1 is disadvantageously limited, as the second holding means applied to the outer sleeve must always be adapted to the dimensions of the first holding means of another cup of the same type, and also to the relayed forces. It is not possible to provide the outer sleeve with an optional form, or to alter its form as required. It is also not possible to omit the outer sleeve in case of need without losing the good stacking properties.
In the cup according to the present invention it is provided that a means for holding another cup of the same type is arranged on the bottom skirt, which means can act together with a similar cup when the cup is stacked. The holding means is advantageously formed by the widening. It is advantageously provided that a first holding means is arranged on the interior-defining sleeve, which first holding means can act together with a second holding means applied on the widening of a similar cup when the cup is stacked.
The stackable cup is advantageously produced in a process by means of the following procedural steps:                forming of at least one first means for holding another cup of the same type on the interior-defining sleeve;        forming of a second means for holding on the bottom skirt, which second holding means can act together with a first holding means applied to a similar cup when the cup is stacked.        
The second holding means is hereby arranged on the interior-defining sleeve or on the bottom, or on a bottom skirt connecting the interior-defining sleeve with the bottom. In any case, the second holding means is applied to a component of the cup which is in contact with the fillable interior.
The formation of the first and second holding means in a cup in the form of a prefabricated semi-finished product has the advantage in that the production of a semi-finished product can take place on a standard cup-making machine, downstream of which a device for forming the holding means is arranged.
The cup according to the present invention has the advantage in that, even without an outer sleeve, the cup can be reliably stacked in a stable manner without wedging and easily de-stacked again. If it is provided that the cup should be assigned a heat-insulating outer sleeve, this can be achieved to a great extent independently and free of the limitations of the cup in European patent EP 1 227 042 B1. The forces occurring during stacking are simply relayed within the interior-defining components from the first holding means to the second holding means. An outer sleeve is thus not absolutely necessary. If, however, an outer sleeve is to be provided, it is not loaded by the forces occurring during stacking. The bottom skirt, by means of which the interior-defining sleeve is connected to the bottom, is a very stable part of the cup and is very well suited to taking up the forces. The forces occurring during stacking are relayed essentially by the interior-defining sleeve from the first holding means to the second holding means, which second holding means can be formed by the widening of the bottom skirt. This permits the formation of a very stable stack comprising a large number of cups, which do not become wedged inside one another even when the stack is subjected to knocks or is for example placed abruptly on the ground. The bottom and the interior-defining sleeve are in any case strong enough to take up the forces occurring during stacking, as they also must take up the forces occurring during filling.
In order to prevent a number of cups wedging during stacking it is advantageous that the dimensions of the second holding means are adapted to the dimensions of the first means for holding another cup of the same type. The first means for holding another cup of the same type can hereby be optionally formed. It is, however, essential that a contour is formed which can take up forces acting in the axial direction of the cup, that is, the forces which act between two cups during stacking. The first holding means is advantageously designed as a bead or a rib, which is at least formed in one area along the circumference of the interior-defining sleeve. The bead or rib can be designed continuously along the circumference or with interruptions.
If, in an embodiment of the present invention, it is provided that the cup comprises a heat-insulating outer sleeve, the design of the heat-insulating outer sleeve is hereby optional. The outer sleeve can for example be made of synthetic, paper or composite material. In order to improve the insulation effect, the outer sleeve can also be corrugated, fluted, embossed or comprise a foam layer. The outer sleeve can be designed as a multi-layered sleeve, for example a corrugated intermediary layer can be provided, which is then covered over by a smooth outer layer. As the cup according to the present invention can be stacked independently of the type of outer sleeve, one and the same inner cup can be combined in a simple and almost endless variety of ways with a variety of outer sleeves. Without changing the shape and dimensions of the inner cup or the components forming the fillable interior, a variety of cups having various optical and haptical designs can be created, owing to the fact that the appearance of the cup as seen by the consumer is mainly defined by the design of the outer sleeve.
In a process for manufacturing a double-walled cup, the following procedural steps are advantageously executed:                forming of at least one first means for holding another cup of the same type on the sleeve defining the interior;        sliding on of an outer sleeve over the interior-defining conical sleeve;        fixing the outer sleeve to the interior-defining sleeve        forming of a second holding means at the bottom skirt, which second holding means can act together with a first holding means applied to a similar cup when the cup is stacked.        
The fixing of the outer sleeve on the inner sleeve can take place for example by means of sealing or gluing. This effects a secure connection between the outer sleeve and the interior-defining sleeve, so that the outer sleeve is reliably prevented from slipping, even if the outer sleeve has only a low height.
In order to achieve a good appearance of the cup, it is advantageous that the outer sleeve ends below the first means for holding another cup of the same type, or even below the bottom. The first holding means applied to the inner sleeve is thus covered over by the outer sleeve and is no longer visible from the outside. Furthermore, it is advantageous when the outer sleeve ends above the widening of the bottom skirt. The widening of the bottom skirt can thus be achieved by means of the action of tools, one arranged outside and one arranged inside of the bottom skirt, without the outer sleeve, which is already slid onto the interior-defining sleeve, hindering the forming of the widening. The widening can, as a result, be very exactly formed. In order that space remains below the outer sleeve for placing the tool there, a distance of more than one millimeter, in particular of more than 2 mm, is provided between the outer sleeve and the widening.
The widening is advantageously spread outwards to such a degree that a parallel to the interior-defining sleeve disposed on the lower edge of the widening, extends at a certain distance outside of the interior-defining-sleeve. In order that a provided outer sleeve does not prevent the stacking of the cups, it is advantageous that the outer contours of the outer sleeve are located within the parallel to the interior-defining sleeve, which parallel is disposed on the widening of the bottom skirt.